The group had its origins in 9to5 News, a newsletter that was first published in December 1972. About a year later, the newsletter's publishers announced the formation of Boston 9to5, a grassroots collective for women office workers that addressed issues such as low pay and lack of opportunities for advancement. One of the organization's earliest victories included a class-action suit filed against several Boston publishing companies that awarded the female plaintiffs $1.5 million in back pay. In 1977 Boston 9to5 joined forces with several like-minded associations to create the Working Women Organizing Project, a national organization headed by Karen Nussbaum, one of Boston 9to5's founders. Nussbaum enlisted the cooperation of the Service Employees International Union (SEIU) and formed Local 925 of the SEIU in Boston to gain for office workers the advantages of collective bargaining.

After several name changes, the organization adopted its current name in 1983, and "9to5, National Association of Working Women", evolved into the largest membership organization of working women in the United States. During the 1980s and '90s, 9to5 focused on issues such as the effects of automation, pay inequities, medical leave, and racial and sexual harassment and discrimination. The organization effectively used the media and lobbied legislators as part of a campaign to warn the public of the health dangers of video display terminals (also known as VDTs) and has also used the media to draw attention to several sexual harassment cases in the 1990s.

As part of its educational efforts, 9to5 established the Job Retention Project in 1987 to assist office workers in developing time-management, goal-setting, and problem-solving skills. In addition, the organization publishes fact sheets, newsletters, and books, such as The Job/Family Challenge: A 9to5 Guide (1995), by Ellen Bravo, that keep workers abreast of current issues. The organization is headquartered in Milwaukee, Wisconsin.